Q. Pumping at joints in concrete carriageway?

Pumping at joints in concrete carriageway takes place in the presence of the below factors:

(i)  Fine-grained subgrade

(ii) Seepage of water in subgrade due to improper or inadequate drainage design

(iii)The presence of heavy vehicular loads 

It includes the pumping out of water-borne particles of the subgrade due to the deflections at the end of concrete slab. First mechanism of pumping involves the softening of subgrade by water and reduction in bearing capacity. It causes a larger instantaneous deflection at the slab ends under heavy traffic loads. At the times of deflection, water containing fine soil particles is pumped out at the joints. So voids are formed in subgrade region and void size grows by repeating the above sequence.